Power module package having improved heat dissipating capability

CROSS-REFERENCE TO RELATED APPLICATIONS

0001This application is a Divisional application and claims priority from U.S. Patent Application Ser. No. 10/167,067 filed Jun. 10, 2002 now U.S. Pat. No. 7,061,080 entitled POWER MODULE PACKAGE HAVING IMPROVED HEAT DISSIPATING CAPABILITY which is hereby incorporated by reference, as if set forth in full in this document, for all purposes.

BACKGROUND OF THE INVENTION

00021. Field of the Invention

0003The present invention relates to a semiconductor package, and more particularly, to a power module package having improved heat dissipating capability.

00042. Description of the Related Art

0005In general, in semiconductor packages, one or more semiconductor chips is or are mounted on a chip pad in a lead frame, encapsulated with an epoxy molding compound (EMC) to protect internal parts, and mounted on a printed circuit board (PCB).

0006However, as high speed, large scale and highly integrated electronic devices have been rapidly developed in recent times, techniques that allow for low cost, miniaturization, and lightweight manufacturing are also required for power devices which are applied to automobiles, industrial equipment and household electrical appliances. Further, the power devices require high reliability and good temperature characteristics. Thus, a power module package for mounting a plurality of semiconductor chips on a semiconductor package is commonly used.

0007<figref idref="DRAWINGS">FIG. 1</figref> is a sectional view of a conventional power module package, which is disclosed in U.S. Pat. No. 5,703,399, published on May 15, 1996, titled “Semiconductor Power Module”.

0008Referring to <figref idref="DRAWINGS">FIG. 1</figref>, the power module package has a structure in which a plurality of semiconductor chips, including a power circuit <b>9</b> and a control circuit <b>8</b>, are mounted on a lead frame <b>3</b>. In the drawing, reference numerals <b>1</b>, <b>2</b>, and <b>4</b><i>a </i>denote a heat sink, an epoxy molding compound (EMC) having a high heat conductivity, and a power circuit chip, respectively. Also, reference numerals <b>5</b><i>a</i>, <b>5</b><i>b</i>, <b>6</b><i>a</i>, <b>6</b><i>b</i>, and <b>7</b> denote a control circuit chip, a resistance component, an aluminum wire, a gold wire, and an insulating EMC, respectively.

0009In the power module package having the above structure, the EMC <b>2</b> having high heat conductivity is used such that the heat sink <b>1</b> which is made of copper is slightly spaced apart from the lead frame <b>3</b>. Thus, the EMC <b>2</b> and the heat sink <b>1</b> dissipate heat, which is generated in the power circuit chip <b>4</b><i>a</i>, to the outside of the power module package. However, the above-mentioned prior art has the following problems.

0010First, the EMC <b>2</b> is filled between the backside of the lead frame <b>3</b> and the heat sink <b>1</b> made of copper in order to maintain insulation properties, and thus there is a limitation in completely dissipating heat generated in the power circuit chip <b>4</b><i>a</i>, to the outside of the power module package. Second, two EMCs having different characteristics are used in one power module package, and thus a process of manufacturing the power module package becomes complicated and it is difficult to perform the process of manufacturing the power module package automatically. Third, the heat sink <b>1</b> made of copper is used in the power module package, and a process of manufacturing the power module package is complicated, and thus a manufacturing cost is increased.

SUMMARY OF THE INVENTION

0011To solve the above problems, it is an object of the present invention to provide a power module package which more effectively dissipates heat generated in a power circuit chip and is simpler and cheaper to manufacture.

0012Accordingly, to achieve the above object, according to an embodiment of the present invention, there is provided a power module package. The power module package includes a power circuit, a control circuit which is connected to the power circuit and controls chips in the power circuit, a lead frame having external connecting means at the edges thereof, a down set part, namely, downwardly facing concave portion, formed between the external connecting means, a first surface to which the power circuit and the control circuit are attached, and a second surface used as a heat dissipating path, wherein the power circuit is attached to the down set part, a heat sink which is closely attached to the down set part of the second surface of the lead frame by an adhesive, and an epoxy molding compound (EMC) for surrounding the power circuit, the control circuit, the lead frame and the heat sink, and for exposing the external connecting means of the lead frame and a side of the heat sink.

0013It is preferable that the power circuit includes power circuit chips and an aluminum wire for connecting the power circuit chips to the lead frame, and the aluminum wire has the diameter of 250–500 μm.

0014It is also preferable that the control circuit includes control circuit chips and a gold wire for connecting the control circuit chips to the lead frame.

0015It is also preferable that the adhesive for attaching the lead frame to the heat sink is a high temperature tape, and the high temperature tape is formed of a material selected from the group consisting of alumina (Al₂O₃), aluminum nitride (AIN), silicon oxide (SiO₂), and beryllium oxide (BeO), and the high temperature tape has a thickness of 10–20 μm. The high temperature tape can comprise particles including such thermally conductive materials embedded in a medium such as a polymer medium.

0016It is also preferable that the adhesive for attaching the lead frame to the heat sink is high temperature solder, and the high temperature solder is formed of a metal material selected from Pb/Sn, Sn/Ag, and Pb/Sn/Ag.

0017It is also preferable that the adhesive for attaching the lead frame to the heat sink is high thermal liquid epoxy, and the thickness of the high thermal liquid epoxy is 3–7 μm.

0018It is also preferable that the heat sink is made of plastic or ceramic, and the heat sink made of plastic or ceramic is formed of a material selected from the group consisting of alumina (Al₂O₃), aluminum nitride (AIN), silicon oxide (SiO₂), and beryllium oxide (BeO), and the heat sink made of plastic or ceramic has a thickness of 1–3 mm.

0019In order to achieve the above object, according to another embodiment of the present invention, there is provided a power module package. The power module package includes a direct bonding copper (DBC) substrate, a power circuit which is attached to the DBC substrate, a lead frame which is connected to one end of the DBC substrate, a control circuit which is attached to the lead frame, a wire for electrically connecting the power circuit and the control circuit to the lead frame, and an epoxy molding compound (EMC) for exposing only the back side of the DBC substrate and part of the lead frame and completely sealing the other portions of the DBC substrate and the lead frame.

BRIEF DESCRIPTION OF THE DRAWINGS

0020The above objects and advantages of the present invention will become more apparent by describing in detail a preferred embodiment thereof with reference to the attached drawings in which:

0021<figref idref="DRAWINGS">FIG. 1</figref> is a sectional view illustrating an example of a conventional power module package;

0022<figref idref="DRAWINGS">FIG. 2</figref> is a sectional view of a power module package according to an embodiment of the present invention;

0023<figref idref="DRAWINGS">FIG. 3</figref> is a sectional view of a power module package according to another embodiment of the present invention;

0024<figref idref="DRAWINGS">FIG. 4</figref> is a sectional view of a power module package according to still another embodiment of the present invention;

0025<figref idref="DRAWINGS">FIG. 5</figref> is a sectional view of the structure of a bottom mold die of a molding equipment used in a method for manufacturing the power module package according to the present invention;

0026<figref idref="DRAWINGS">FIG. 6</figref> is a sectional view illustrating a sealing process of the method for manufacturing the power module package according to the present invention; and

0027<figref idref="DRAWINGS">FIGS. 7A through 7D</figref> are sectional views illustrating the method for manufacturing the power module package according to another embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

0028Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

0029The arrangement of a power circuit element and a control circuit element which will be described in this specification, and the structure of a lead frame and a heat sink are exemplified, however, this invention is not limited to only the specific shapes shown in drawings and is self-evident to a person skilled in the art.

0030<figref idref="DRAWINGS">FIG. 2</figref> is a sectional view of a power module package according to an embodiment of the present invention. Referring to <figref idref="DRAWINGS">FIG. 2</figref>, the power module package <b>200</b> includes a lead frame <b>210</b>, a power circuit element <b>220</b>, a control circuit element <b>230</b>, a heat sink <b>250</b>, and an epoxy molding compound (EMC) <b>270</b>. The power circuit element <b>220</b> includes a power circuit chip <b>221</b> and an aluminum wire <b>222</b>. The aluminum wire <b>222</b> has a diameter of about 250–500 μm such that the aluminum wire <b>222</b> can withstand a high current rating. The control circuit element <b>230</b> includes a control circuit chip <b>231</b> and a gold wire <b>232</b>. The aluminum wire <b>222</b> and the gold wire <b>232</b> connect the power circuit chip <b>221</b> to the control circuit chip <b>231</b>.

0031The lead frame <b>210</b> has a first surface <b>211</b> onto which circuit elements are attached and a second surface <b>212</b> which is opposite to the first surface <b>211</b>, and a down set part <b>240</b>, namely, a downwardly facing concave portion, is formed in the middle of the lead frame <b>210</b>. The down set part <b>240</b> may be exactly placed in the center so that both sides thereof are symmetrical, but may be formed to be off to one side. The power circuit element <b>220</b> and the control circuit element <b>230</b> are attached to the first surface <b>211</b> of the lead frame <b>210</b>. In particular, the power circuit element <b>220</b>, which generates a large amount of heat, is attached to the first surface <b>211</b> of the down set part <b>240</b> of the lead frame <b>210</b>.

0032The heat sink <b>250</b> is attached to the second surface <b>212</b> of the down set part <b>240</b> of the lead frame <b>210</b> by a high temperature tape <b>260</b>, and a side of the heat sink <b>250</b> is completely exposed to the outside of the power module package <b>200</b>. As occasion demands, high temperature solder can be used instead of the high temperature tape. Preferably, the solder is formed of a metal material selected from Pb/Sn, Sn/Ag, and Pb/Sn/Ag.

0033The heat sink <b>250</b> has a thickness of about 1–3 mm and can be manufactured by using a material selected from the group consisting of alumina (Al₂O₃), aluminum nitride (AIN), silicon oxide (SiO₂), and beryllium oxide (BeO). For example, a heat sink <b>250</b> made of ceramic can be manufactured by adding a material from the group consisting of alumina (Al₂O₃), aluminum nitride (AIN), silicon oxide (SiO₂), and beryllium oxide (BeO) to a filling material including ceramic. Also, a heat sink <b>250</b> made of plastic can be manufactured by adding a material from the group consisting of alumina (Al₂O₃), aluminum nitride (AIN), silicon oxide (SiO₂), and beryllium oxide (BeO) to a filling material including plastic. Meanwhile, if solder is used instead of the high temperature tape, metal is formed on a side of the heat sink <b>250</b> to be attached to the lead frame <b>210</b>. Similarly, the high temperature tape <b>260</b> can be manufactured by using a material from the group consisting of alumina (Al₂O₃), aluminum nitride (AIN), silicon oxide (SiO₂), and beryllium oxide (BeO) and has a thickness of about 10–20 μm such that the lead frame <b>210</b> and the heat sink <b>250</b> are completely attached to each other.

0034According to the power module package having the above structure, the heat dissipating effect is increased because there is no space between the down set part <b>240</b> of the lead frame <b>210</b> and the heat sink <b>250</b>.

0035<figref idref="DRAWINGS">FIGS. 5 and 6</figref> illustrate a method for manufacturing the power module package according to an embodiment of the present invention. Specifically, <figref idref="DRAWINGS">FIG. 5</figref> is a sectional view of the structure of a bottom mold die of a molding apparatus used in a method for manufacturing the power module package according to the present invention, and <figref idref="DRAWINGS">FIG. 6</figref> is a sectional view illustrating a sealing process of the method for manufacturing the power module package according to the present invention.

0036Referring to <figref idref="DRAWINGS">FIGS. 2</figref>, <b>5</b> and <b>6</b>, first, the lead frame <b>210</b> having the down set part <b>240</b> formed in the middle thereof is prepared. The power circuit chip <b>221</b> and the control circuit chip <b>231</b> are attached to the first surface <b>211</b> of the lead frame <b>210</b> by performing a die attach process. The power circuit chip <b>221</b> is attached to part of the down set part <b>240</b> of the lead frame <b>210</b>. Next, a wire bonding process is performed, thereby properly connecting the power circuit chip <b>221</b> to the control circuit chip <b>231</b>. The gold wire <b>232</b> is used as a wire for the control circuit chip chip <b>231</b>, and the aluminum wire <b>222</b> is used as a wire for the power circuit chip <b>221</b>. Preferably, the aluminum wire <b>222</b> has a diameter of about 250–500 μm such that the aluminum wire <b>222</b> can withstand a high current rating. Bonding methods such as a wedge bonding method and a ball bonding method, are used in performing the wire bonding process. In order to perform the wire bonding process smoothly, it is preferable that the aluminum wire <b>232</b> is first bonded and then the gold wire <b>222</b> is bonded.

0037Next, the heat sink <b>250</b> is fixed in a groove <b>524</b> which is formed on a heat sink block <b>522</b> of the bottom mold die (<b>520</b> of <figref idref="DRAWINGS">FIG. 5</figref>). The heat sink <b>250</b> has a thickness of about 1–3 mm and can be manufactured by using a material selected from the group consisting of alumina (Al₂O₃), aluminum nitride (AIN), silicon oxide (SiO₂), and beryllium oxide (BeO). For example, the heat sink made of ceramic can be manufactured by adding a material from the group consisting of alumina (Al₂O₃), aluminum nitride (AIN), silicon oxide (SiO₂), and beryllium oxide (BeO) to a filling material including ceramic. Also, the heat sink <b>250</b> made of plastic can be manufactured by adding a material from the group consisting of alumina (Al₂O₃), aluminum nitride (AIN), silicon oxide (SiO₂), and beryllium oxide (BeO) to a filling material including plastic.

0038Next, after the wire bonding process, the lead frame <b>210</b> is placed in a molding apparatus. Here, the heat sink <b>250</b> has already been fixed in the groove <b>524</b> of the bottom mold die <b>520</b>. Subsequently, the high temperature tape <b>260</b> is melted such that the heat sink <b>250</b> is completely attached to the second surface <b>212</b> of the down set part <b>240</b> of the lead frame <b>210</b>. Here, the temperature and pressure for melting the high temperature tape <b>260</b> are about 160–220° C. and about 30 kg/cm², respectively. The high temperature tape <b>260</b> can be manufactured by using a material selected from the group consisting of alumina (Al₂O₃), aluminum nitride (AIN), silicon oxide (SiO₂), and beryllium oxide (BeO) and has a thickness of about 10–20 μm.

0039Next, a top mold die <b>510</b> is lowered, and the EMC <b>270</b> is flowed into an EMC apparatus through a gate <b>530</b>. The EMC <b>270</b> is changed into a liquid by heat and pressure. Thus, the EMC <b>270</b> flows in a direction indicated by the arrows and fills the inside of a mold <b>500</b> uniformly. A transfer molding equipment including a plurality of gates and runners is used as the molding equipment, and preferably, the temperature for a sealing process is about 160–170° C.

0040Next, the lead frame after the sealing process, that is, the power module package <b>500</b>, is unloaded from the molding apparatus, then the heat sink <b>250</b> is completely attached to the second surface <b>212</b> of the down set part <b>240</b> of the lead frame <b>210</b> by using the high temperature tape <b>260</b>. Subsequently, subsequent processes such as a trim process and a forming process are performed.

0041<figref idref="DRAWINGS">FIG. 3</figref> is a sectional view of a power module package according to another embodiment of the present invention. Referring to <figref idref="DRAWINGS">FIG. 3</figref>, the power module package <b>300</b> includes a lead frame <b>310</b>, a power device <b>320</b>, a control device <b>330</b>, a heat sink <b>350</b>, and an epoxy molding compound (EMC) <b>370</b>. The power device <b>320</b> includes a power circuit chip <b>321</b> and an aluminum wire <b>322</b>. The control device includes a control circuit chip <b>330</b> and a gold wire (not shown). The lead frame <b>310</b> has a thickness of about 0.5–1.0 mm and includes a down set part <b>340</b> that is formed in the middle of the lead frame <b>310</b>. The power device <b>320</b> and the control device <b>330</b> are attached to one surface of the lead frame <b>310</b>. In particular, the power device <b>320</b>, which generates a large amount of heat, is attached to the down set part <b>340</b> of the lead frame <b>310</b>.

0042The heat sink <b>350</b> is attached to the opposite surface of the down set part <b>340</b> of the lead frame <b>310</b> using high thermal liquid epoxy <b>360</b>, and a side of the heat sink <b>350</b> is completely exposed to the outside of the power module package <b>300</b>. The high thermal liquid epoxy <b>360</b> can be made by adding a filling material including a material from the group consisting of alumina (Al₂O₃), aluminum nitride (AIN), silicon oxide (SiO₂), and beryllium oxide (BeO) to epoxy. The thickness of the high thermal liquid epoxy <b>360</b> is about 3–7 μm and represents thermal resistance less than about 1.5° C./W, and thus has improved thermal conductivity in comparison with a conventional power module package in which epoxy molding compounds are used.

0043<figref idref="DRAWINGS">FIGS. 7A through 7D</figref> are sectional views illustrating the method for manufacturing the power module package according to another embodiment of the present invention. First, referring to <figref idref="DRAWINGS">FIG. 7A</figref>, the lead frame <b>310</b> having a thickness of about 0.5–1.0 mm is prepared. The power circuit chip <b>321</b> and the control circuit chip <b>330</b> are attached to the surface of the lead frame <b>310</b> by performing a die attach process. The power circuit chip <b>321</b> is attached to part of the down set part <b>340</b> of the lead frame <b>310</b>. The die attach process may be performed using solder or silver (Ag) epoxy as an adhesive. In a case where the die attach process is performed using solder as an adhesive, the temperature and pressure for the die attach process is about 350–380° C. and about 3–5 kg/cm², respectively, and the die attach process is performed in a hydrogen atmosphere. In a case where the die attach process is performed using Ag epoxy as an adhesive, the die attach process is performed at the room temperature and pressure under about 1–2 kg/cm².

0044Next, referring to <figref idref="DRAWINGS">FIG. 7B</figref>, the high thermal liquid epoxy <b>360</b> is attached to the upper surface of the heat sink <b>350</b> made of ceramic having a thickness of about 1–3 mm. The high thermal liquid epoxy <b>360</b> can be made by adding a filling material including a material from the group consisting of alumina (Al₂O₃), aluminum nitride (AIN), silicon oxide (SiO₂), and beryllium oxide (BeO) to epoxy.

0045Next, referring to <figref idref="DRAWINGS">FIG. 7C</figref>, the heat sink <b>350</b> made of ceramic is attached to the lead frame <b>310</b> onto which the power circuit chip <b>321</b> is attached, using the high thermal liquid epoxy <b>360</b> as an adhesive. The attach process is performed at a temperature of about 150–180° C. and pressure under about 0.5–1.0 kg/cm²for about 3–5 minutes.

0046Next, referring to <figref idref="DRAWINGS">FIG. 7D</figref>, an aluminum wire bonding process or gold wire bonding process is performed, thereby electrically connecting the power circuit chip <b>321</b> to the lead frame <b>310</b>, the power circuit chips <b>321</b> to each other and the control circuit chip <b>330</b> to the lead frame <b>310</b>. Wires <b>322</b> including gold wires and aluminum wires. The gold wire is used as a wire for the control circuit chip <b>330</b>, and aluminum wires are used as wire for the power circuit chips <b>321</b>. The aluminum wire bonding process is performed by wedge bonding, and the gold wire bonding process is performed by ball bonding.

0047Next, as shown in <figref idref="DRAWINGS">FIG. 3</figref>, an encapsulation process is performed such that only the lower surface of the heat sink <b>350</b> made of ceramic and the end part of the lead frame <b>310</b> are exposed by the EMC <b>370</b>, and then, general trim and forming processes are performed.

0048<figref idref="DRAWINGS">FIG. 4</figref> is a sectional view of a power module package according to still another embodiment of the present invention. The power module package according to the present embodiment is different from the power module packages according to the previous embodiments in which a heat sink is used, in that a direct bonding copper (DBC) substrate is used in the power module package according to the present embodiment.

0049Referring to <figref idref="DRAWINGS">FIG. 4</figref>, the power module package <b>400</b> includes a lead frame <b>410</b>, a power device <b>420</b>, a control device <b>430</b>, a DBC substrate <b>450</b>, and an epoxy molding compound (EMC) <b>470</b>. The power device <b>420</b> includes a power circuit chip <b>421</b> and an aluminum wire <b>422</b>. The control device includes a control circuit chip <b>430</b> and a gold wire (not shown). The DBC substrate <b>450</b> is comprised of central ceramic <b>451</b>, an upper copper layer <b>452</b> attached to the upper surface of the ceramic <b>451</b>, and a lower copper layer <b>453</b> attached to the lower surface of the ceramic <b>451</b>. The power circuit chip <b>421</b> is attached to the surface of the upper copper layer <b>452</b> of the DBC substrate <b>450</b>. The lead frame <b>410</b> is connected to the upper copper layer <b>452</b> of the DBC substrate <b>450</b>. The control circuit chip <b>430</b> is attached to the lead frame <b>410</b>.

0050A DBC substrate having higher thermal conductivity is used in the power module package <b>400</b>, and thus the power module package <b>400</b> has improved heat dissipating capability.

0051In order to manufacture the power module package <b>400</b>, first, the lead frame <b>410</b> is attached to the DBC substrate <b>450</b>. The attach process may be performed using an adhesive such as solder or thermal tape, or by welding using a laser or spot, or by thermal compression using silver (Ag) or Ag/Sn plating. Next, the power circuit chip <b>421</b> and the control circuit chip <b>430</b> are attached to the lead frame <b>410</b>. The die attach process may be performed using solder and Ag epoxy. The solder is used to attach the power circuit chip <b>421</b> to the lead frame <b>410</b>, and in this case, the die attach process is performed at a temperature of about 330–360° C. The Ag epoxy is used to attach the control circuit chip <b>430</b> to the lead frame <b>410</b>, and in this case, the die attach process is performed at the room temperature. Next, the power circuit chip <b>421</b> and the control circuit chip <b>430</b> are electrically connected to the lead frame <b>410</b> by performing a wire bonding process. An aluminum wire is used as a wire for the power circuit chip <b>421</b>, and a gold wire is used as a wire for the control circuit chip <b>430</b>. Next, an encapsulation process is performed using the EMC <b>470</b>, and then, general trim and forming processes are performed.

0052As described above, the power module package and the method for manufacturing the same according the present invention have the following effects.

0053First, since the heat sink is directly attached to the back side of the down set part of the lead frame by using the high temperature tape, heat which is generated during operation of the power module package can be effectively dissipated, thereby increasing the reliability of the power module package. As an example, when the structure and material of the heat sink of the power module package are changed like those in the prevention invention, RΘ_jc, as the thermal resistance of the conventional power module package was measured to be 0.19° C./Watt. On the other hand, RΘ_jcof the power module package according to the present invention was measured to be 0.15° C./Watt, and as a result, the heat dissipating capability is improved by 20–30%. For reference, RΘ_jcis an index representing a difference in temperature from the PN junction of the power circuit chip <b>121</b> to a case, as a mold line. Similarly, RΘ_jc, was measured to be 0.15° C./Watt even in a case where the high thermal liquid epoxy instead of the high temperature tape is used.

0054Second, since the sealing process for the power module package is performed at a time by using the EMC having the same heat conductivity, it is advantageous to simplify and automatize processes.

0055Third, the power module package is manufactured by using the heat sink (not metal) at a low cost and the processes are simplified, thereby reducing the manufacturing cost of the power module package.

0056While this invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.